Urine: the ultimate 'organic' fertiliser?

Your bladder's loss could be your vegetable garden's gain, since urine makes for a surprisingly good fertiliser - so why are we wasting our wee?

Ever felt the urge to skip the toilet and just pee in the bush, behind the tree, in the flowerbed? Have you ever wondered why we have been so conditioned to hold on to a screaming bladder while we search for the nearest toilet, which could be many minutes away, meanwhile putting certain internal organs through extreme stress?

There are public decency laws to respect, and for women there are obvious added complications surrounding the degree of derobing that may be necessary, but we shouldn't be wasting this ultimate homemade fertiliser. Most of us may have a deeply ingrained belief that urine is a noxious substance that must be disposed of in a urinal, but this is a myth that needs busting.

Urine for a pleasant surprise

Human urine is one of the fastest-acting, most excellent sources of nitrogen, phosphorous, potassium and trace elements for plants, delivered in a form that’s perfect for assimilation. Not only that, we all have a constant, year-round supply of it - and it's free!

Fresh human urine is sterile and so free from bacteria. In fact it is so sterile that it can be drunk when fresh; it’s only when it is older than 24 hours that the urea turns into ammonia, which is what causes the 'wee' smell. At this stage it will be too strong for use on plants, but poured neat on to the compost heap it makes a fabulous compost accelerator/activator, with the extra benefit of adding more nutrients.

Dilute one part urine to 10-15 parts water for application on plants in the growth stage. Dilute in 30-50 parts water for use on pot plants, which are much more sensitive to fertilisers of any kind. Trees, shrubs and lawns are fine with undiluted urine, but for obvious reasons apply it underneath fruiting bushes, as opposed to directly on to foliage and fruit. Some fertilisers, such as seaweed, are specifically used as foliar feeds [applied direct to leaves], but urine is always best applied directly to a plant's root system.

Antibiotics, vitamin supplements and other medications will end up in your urine, but in such minute quantities as to be negligible, especially when diluted in water.

What is wee?

Urine is 95 per cent water, 2.5 per cent of which is urea, and a further 2.5 per cent of which is a mixture of minerals, salts, hormones and enzymes. It is a blood byproduct but despite containing some bodily waste is non-toxic.

During a pee, a healthy adult will release 11g nitrogen/urea, 1g phosphorus/super-phosphate and 2.5g potassium. Patrick Makhosi, a soil scientist with Uganda's Kawanda Agricultural Research Organisation, confirms the efficacy of human urine as a fertiliser. He says that applying urine to growing vegetables once every week for at least two months will more than double the yield.

Flushed with embarrassment

Many toilets use between 50 and 100 litres of water a day to flush approximately 1.5 litres of pee. The average person has five wees a day and the average flush uses eight litres of water - that's 40 litres. Given that the population of the UK is an estimated 62 million, we may be contaminating and then flushing away somewhere in the region of 2,500 million litres of clean drinking water every day. (Returning our waste water to a drinkable condition also involves a complicated process of chemical separation and cleaning.) If this were an action by a commercial company, serious questions would be asked about its practices. Diluting urine to use as a fertiliser would use a fraction of this amount of water while producing a valuable plant food.

Using urine instead of disposing of it also cuts down on river pollution: urine is a major source of nitrogen, which, if an expensive denitrification process is not undertaken at the water treatment plant, can contribute to river eutrophication. Excessive levels of nutrients in our effluent systems leads to the growth of algae. Algal blooms can ultimately causes the death of plants and animals throughout our waterways.

So, if you want a ready source of plant food that is perfectly balanced for your garden, that is absolutely free, available all year round, saves valuable drinking water and excessive use of cleaning chemicals, and limits the heavy use of fossil fuels in artificial fertiliser production, consider using your own urine.

There is also the added pleasure of feeling that you are a more integrated part of the cycle of growth in your garden; in the loop, not exempted from it. Happy gardening - and remember these golden rules...

Keep it separateSeparate urine from other bodily waste to keep it sterile. Pee in a bottle or bucket, or invest in a urine-separating toilet.

Use it freshThe smell of ammonia also indicates a drop in nutritional content. Use old wee directly on your compost heap

Always diluteUrine is too strong to be used neat on plants. Dilute at least 10:1 and up to 50:1 for use on tender plants and seedlings.